Conventionally electronic verification of variably printed data is accomplished utilizing digitizing cameras. For example such as shown in U.S. Pat. Nos. 4,685,139 and 5,384,859, a reference level for acceptability of imaged data is determined and stored in a computer, and sometimes long afterwards a digitizing camera views subsequently printed webs or sheets and compares the subsequent imaging to the reference data. While such a system can effectively determine whether the intended imaging produced by a printer has been applied to a web or sheet, such systems are slow (e.g. web or sheet speed of well less than 200 feet per minute), very expensive, and do not truly provide real time evaluation.
According to the present invention a method and system are provided for verifying the intended imaging produced by a printer in a substantially real-time, relatively inexpensive, and high speed (variable from 0 to X) manner. According to the invention, data to be printed is sent from a computer control to a raster image processor (RIP) which converts it to a bitmap. The bitmap is sent both to the printer and to a print monitor. The printer images the bitmap on a moving web or sheet (e.g. moving at the speed of about 200-300 feet per minute), and downstream of the printer a first sensor in the form of a linear photodiode array can scan substantially every pixel across the width of the web or sheet. The scanned area may be illuminated by a lamp. The scanned information is fed to the print monitor where it is compared to the bitmap. Also a second linear photodiode array may be provided before the printer and the data therefrom fed to the print monitor so that the combination of the bitmap and the data from the second sensor may be compared to the imaging scanned by the first scanner. If the print monitor determines that there is a significant discrepancy, that data is transmitted back to the computer control which then can be used to log bad forms, generate a human recognizable signal (such as a sound or warning light), or shut down the system. The system according to the present invention is relatively inexpensive, linear digital photosensor arrays (linear photodiode arrays) being much less expensive than digitizing cameras, and the system is essentially real-time because the sensed imaging is not compared to a reference determined at some perhaps long ago previous point in time, but rather is compared to a recently generated bitmap.
According to one aspect of the present invention there is provided a method of verifying the intended imaging produced by a printer, using a print monitor, comprising: (a) Generating electronic print data, e.g. a bitmap, for controlling the printer. (b) Substantially simultaneously supplying the electronic bitmap to the printer and to the print monitor. (c) Moving a web or sheet in a first direction to and past the printer. (d) Imaging the moving web or sheet with the printer as the web or sheet moves past the printer. (e) Scanning the web or sheet at a location past the printer to sense the imaging thereof in electronic format. And, (f) supplying the sensed imaging in electronic format from (e) to the print monitor and comparing it to the electronic bitmap supplied to the print monitor in (b).
In the invention (e) is typically practiced utilizing an opto-electronic array, e.g., a linear photodiode array. The web or sheet image area preferably has an effective width x, and the linear photodiode array has an effective length at least approximately equal to x, and (e) is practiced to scan substantially every pixel across the web or sheet image area width.
The method may further comprise (g) scanning the web or sheet at a location before the printer to sense the content of the pixels prior to imaging; (h) supplying the sensed data from (g) in electronic format to the print monitor; and practicing (f) to compare the data from (e) to the combination of the data from (h) and the electronic bitmap supplied to the print monitor in (b). Further the method may comprise (i) if the practice of (f) indicates a discrepancy of greater than a predetermined amount generating a signal indicative of the discrepancy. Still further the method may comprise (j), in response to the signal indicative of the discrepancy, logging information which can be used to identify a section of the web or sheet that should be inspected or removed, generating operator warning indicia, or terminating the continued practice of (a)-(d).
In the implementation of the invention (d) may be practiced by inkjet printing the web or sheet, such as utilizing a MICA 2 inkjet array such as disclosed in U.S. patent application Ser. No. 08/661,178 filed May 13, 1996 (the disclosure of which is hereby incorporated by reference herein). Also (a) through (f) may be practiced using business forms as the web or sheet, which may have non-variable printing while the inkjet printer prints variable data. Also, (a) through (f) may be practiced at a speed of web or sheet movement of greater than 200 fpm (e.g. about 200-300 fpm, or all smaller ranges within that broad range).
According to another aspect of the present invention an imaging system is provided comprising: A computer control (e.g. an XL Data System available from Moore U.S.A., Inc. of Lake Forest, Ill.). An electronic print data (e.g. bitmap) generator (e.g. an RIP such as a GRIP-SD+) connected to the computer control. A printer (e.g. a variable indicia printer such as an inkjet array). A print monitor. Means for moving a web or sheet to and past the printer in a given direction (e.g. any conventional rollers, feeders, guides, or like structures conventionally used for handling webs or sheets). A sensor which senses images on the web or sheet, the sensor located past the printer in the direction of web or sheet movement. The electronic print data generator connected to the printer and to the print monitor and supplying electronic print data to both the printer and the print monitor. The sensor connected to the print monitor. And, the print monitor comparing data from the sensor to data from the electronic print data generator to determine any significant discrepancy.
The print monitor is typically connected to the computer control to supply discrepancy information from the print monitor to the computer control. The sensor preferably comprises an opto-electronic array, e.g. a linear photodiode array which has an effective length at least approximately equal to one-sixth inch up to the effective width of the web or sheet image area to sense substantially every pixel; for example the sensor may comprise one or more 200-300 pixel linear photodiode array elements. A lamp (e.g. halogen) connected to a linear fiber optic illuminator may be provided, the illuminator positioned adjacent the sensor for illuminating the web or sheet adjacent the sensor.
The system may further comprise a second optical sensor positioned before the printer in the direction of web movement, the second sensor connected to the print monitor, the print monitor comparing data from the sensor to a combination of data from the electronic print data generator and the second sensor.
According to another aspect of the present invention an imaging system is provided comprising the following components: A printer. A print monitor. Means for moving a web or sheet to and past the printer in a given direction. A first sensor which senses images on the web or sheet, the first sensor located past the printer in the direction of web or sheet movement. An electronic print data generator connected to the printer and to the print monitor and supplying electronic print data to both the printer and the print monitor. A second sensor which senses images on the web or sheet prior to the web or sheet passing to the printer. The first and second sensors connected to the print monitor. And, the print monitor comparing data from the first sensor to data from the electronic print data generator and the second sensor combined to determine any significant discrepancy. The details of the components may be as described above.
It is the primary object of the present invention to provide a simple, cost-effective, accurate, and high speed method and system for verifying the intended imaging produced by a printer on a moving web or sheet. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.